1. Field of the Invention
The present invention relates to fibre channel systems, and more particularly, to determining frame time out to minimize frame latency and reduce congestion.
2. Background of the Invention
Fibre channel is a set of American National Standard Institute (ANSI) standards, which provide a serial transmission protocol for storage and network protocols such as HIPPI, SCSI, IP, ATM and others. Fibre channel provides an input/output interface to meet the requirements of both channel and network users.
Fibre channel supports three different topologies: point-to-point, arbitrated loop and fibre channel fabric. The point-to-point topology attaches two devices directly. The arbitrated loop topology attaches devices in a loop.
The fibre channel fabric topology attaches host systems directly to a fabric, which are then connected to multiple devices. The fibre channel fabric topology allows several media types to be interconnected.
Fibre channel is a closed system that relies on multiple ports to exchange information on attributes and characteristics to determine if the ports can operate together. If the ports can work together, they define the criteria under which they communicate.
In fibre channel, a path is established between two nodes where the path's primary task is to transport data from one point to another at high speed with low latency, performing only simple error detection in hardware.
Fibre channel fabric devices include a node port or “N_Port” that manages fabric connections. The N_port establishes a connection to a fabric element (e.g., a switch) having a fabric port or F_port. Fabric elements include the intelligence to handle routing, error detection, recovery, and similar management functions.
A fibre channel switch is a multi-port device where each port manages a simple point-to-point connection between itself and its attached system. Each port can be attached to a server, peripheral, I/O subsystem, bridge, hub, router, or even another switch. A switch receives messages from one port and automatically routes it to another port. Multiple calls or data transfers happen concurrently through the multi-port fibre channel switch.
Fibre channel switches use memory buffers to hold frames received and sent across a network. Associated with these buffers are credits, which are the number of frames that a buffer can hold per fabric port.
Frames enter a fabric switch element at a given time, but for whatever reason may be stalled in the switch element. This can cause congestion and frame latency causing degradation in the overall performance of the network.
A fibre channel fabric is required to either deliver or discard a frame within certain duration, known as RA_TOV (per fibre channel standard, FC-FS). Error recovery procedures depend on this aspect. Conventional fibre channel switch elements do not know how long a frame has taken to traverse other switch elements in the fabric before arriving at a local switch element.
Therefore, what is required is a method and system for switch elements to track the total time a frame has been in the fabric and declare a time-out if the frame has not been delivered/processed in time.